Novel water soluble cationic acrylamide polymers having relatively uniform cationic quaternary amine functional unit distribution

ABSTRACT

Novel water-soluble, cationic acrylamide polymers characterized by having a weighted standard deviation of the charge distribution, as calculated from measurements of the disappearance ratio of the comonomers, of less than about 0.6 are prepared by acidifying an acrylamide monomer with a weak acid and polymerizing said monomer with a monomer having quaternary amine groups. The polymers are useful as flocculation aids and for a variety of other water treatment applications.

This application is a continuation-in-part of our application Ser. No.761,089 filed Aug. 2, 1985 (now U.S. Pat. No. 4,668,747), which is inturn a continuation-in-part of our Ser. No. 653,253 filed Sept. 24, 1984now abandoned.

This invention relates to the use of acids in conjunction with and toimprove the performance and stability of cationic water soluble watertreatment polymers having a quaternary amine functionality, andcopolymers thereof, with ethylenically unsaturated monomers. Thesepolymers may be prepared by reaction in the presence of free radicalinitiators or ionizing radiation. The resulting polymers have relativelyuniform cationic quaternary amine functional unit distribution to adegree heretofore unobtainable.

In the invention dicarboxylic acid is used to improve the performanceand stability of cationic water treatment polymers. The procedure can beused in both solution and emulsion (water/oil) reactions. Theperformance of water treatment polymers of this kind relates to thedewatering capability of the polymer based on a SFR (specific filterresistance) test of total drainage of the supernatant through the sludgein comparison to dose. Stability relates to the performance of thepolymer and retention of cationic charge.

The performance of cationic polymer can be related to a number ofdifferent variables including: (1) molecular weight, (2) charge, (3)charge distribution. The method of this invention involves the effect onthe charge distribution in the polymer during the course of the reactionthrough the use of a dicarboxylic acid, and buffering capability in thereaction mass to maintain the desired charge in the polymer after thecompletion of the reaction.

The use of these cationic polymers is widespread. They are useful asdrainage aids, flotation aids, retention aids, process waterflocculants, and in the manufacture of paper and paper products, wasteeffluent treatment, oil recovery operations, and mining operations.

The major difficulty in preparing these cationic products relates to thedifferences in reactivity between the acrylamide (the major backbone inthese polymer formulations) and the cationic co-monomers. In the priorart, in an effort to attain better co-monomer distribution in thecopolymer, the cationic co-monomer was added in increments over thecourse of the reaction to prevent the homopolymerization of the cationicmonomer substrate and force the reaction between the monomers present. Asecond problem is the lack of hydrolytic stability of quaternarycationic monomers and the resulting polymers; a means for suppressingthis hydrolytic degradation would therefore be desirable.

Cationic water soluble polymers have been found to be relativelydifficult to produce and apply because of the poor hydrolytic stabilityof the product polymer and in the case of most cationic monomers,difficulties occur in the polymerization because the relativereactivities of the cationic monomers are much higher than the usualcomonomers. The high reactivity of the cationic monomers leads toproduction of an initial fraction during the copolymerization ofmaterial that is excessively high in cationic content and a laterfraction almost devoid of cationic content. Materials polymerized inthis fashion do not exhibit the same application activity as materialsproduced with an even distribution of charge during the polymerization.

The acidification of a mixture containing ethylenically unsaturatedcationic and nonionic monomers is described in U.S. Pat. No. 3,929,751(Gershberg); U.S. Pat. No. 4,195,147 (Sekmakas, et al); and U.S. Pat.No. 4,024,040 (Phalanges, et al.).

The work of Gersberg discloses the addition of sulfuric acid to adjustthe pH of an aqueous phase reaction containing various monomersincluding cationic monomers described in this invention. The pH rangeconsidered optimum for the invention described by Gershberg is clearlyoutside that considered optimum for the present invention and the use ofstrong acids does not give the desirable results of the weaker acidsdisclosed as suitable in the present invention.

Phalanges, et al. discloses polymerization by radiation in the range ofpH 2 to 5 for the purpose of preventing certain aluminum salts fromprecipitating out of solution. These aluminum salts are in solution forthe purpose of preventing crosslinking of the polymer which will occuras the conversion of the monomer nears completion. Phalanges does notdisclose the advantages of any particular type of acid, nor the benefitsof using acids other than those preventing the precipitation of saltspresent in the system of that patentee.

Sekmakas, et al. discloses the use of acids in the preparation oftertiary amine copolymers for use in electrocoating by neutralizing theamine functionality with various acids to a pH in the general range of 5to 7. This pH range is outside the range of interest in the presentinvention. As the functional group involved in Sekmakas, et al., is atertiary amine, the chemical nature of the compounds is completely atvariance with the subject of this invention. In fact, Sekmakas discussesthis possibility and rejects it as not feasible because of the largeamount of acid required to neutralize the amine salt functionality.

A need accordingly exists for a means to enhance the electrolyticstability of the cationic functionality of acrylamide polymers and toimprove the relative reaction rates of acrylamide and the cationiccomonomer to produce polymers having more uniform cationic quaternaryamine functional unit distribution.

SUMMARY OF THE INVENTION

In accordance with the invention, an acid additive is utilized tocontrol the polymerization to produce a more uniform comonomer rate ofreaction and a novel class of polymers having a more uniform cationicquaternary amine functional unit distribution than heretofore obtained.

The presence of acid in the resulting cationic product increases itsshelf life and hydrolytic stability. Particular processing advantagesinclude the elimination of the requirement for continuous feed ofcationic monomer and the resulting potential contamination of thereaction mass with air, and the production of solution gel products ofgood charge distribution where continuous monomer feed is impracticalbecause of the high vicosity and blending difficulties inherent in theproduction of solution gels. Further optimization of the chargedistribution may be possible by varying factors such as the quantity ofacid, the pK_(a) 's of the carboxylic acid(s), the pH of the system, theuse of blends of various carboxylic acids and the use of acids with oneor more carboxylic functionality, even including polymers and oligomersof acrylic acid.

In accordance with the invention, novel polymeric compositions havingexceptionally well distributed and active cationic charges are prepared.A measure of the charge distribution is the weighted standard deviationof the ratio of reacted QM to AM. ##EQU1## and x_(a) is the ratiodQM/dAM at the a^(th) measurement and n_(a) is the percentage of monomerconverted to polymer at the respective ratio. Ideally this ratio wouldbe constant throughout the reaction yielding polymer with constantdistribution of charge and a standard deviation of the ratio of zero.The novel polymers of the invention are inherently characterized byhaving a weighted standard deviation of the charge distribution, ascalculated from measurements of the disappearance rates of the monomersas described above of less than about 0.6 and preferably less than about0.5. Generally, the range of the weighted standard deviation is betweenabout 0.3 and about 0.6 and preferably between about 0.3 and about 0.5.

The novel polymeric compositions of the invention are highly useful inflocculation, sludge dewatering as retention and flotation aids andother water treating applications. These water soluble polymers containsegments of acrylamide or methacrylamide (i.e., derived from monomershaving the formula CH₂ =RC--CONH₂ where R is H or CH₃), acrylic acid ormethacrylic acid, salts thereof, dimethylamino ethyl methyl acrylatequaternary salts, and other ethylenically unsaturated comonomerscontaining quaternary amine functional groups.

Quaternary amine cationic monomers having the formula CH₂ =CHR₁COO(CH₂)_(n) N(CH₃)₃.sup.⊕ R₂.sup.⊖ where R₁ is H or CH₃, n is 2 or 3and R₂ is Cl⁻ or CH₃ OSO₃ ⁻. Typical such monomers include:1-trimethylammonium-2-hydroxypropylmethacrylate methosulfate,trimethylammonium-2-hydroxypropylacrylate methosulfate,1-trimethylammonium-2-2-hydroxypropylacrylate methosulfate,3-methacrylamidopropyltrimethyl-ammonium chloride,dimethylaminoethylmethacrylate methylchloride quaternary salt, and thelike. The repeating monomer units of the polymer will include anywherefrom 1-70 mole % of the cationic monomer with the remainder being anonionic substrate such as: acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide and the like.

The acid employed in the copolymerization may be an organic carboxylicacid as a dicarboxylic acid. Illustrative suitable dicarboxylic acidsare adipic and succinic acids.

An object of the invention is the provision of a process for thedevelopment of novel cationic water soluble polymers having excellentcharge distribution and cationic charge stability. Polymers manufacturedby this process have many advantages over these currently available. Theprimary advantage is improved charge distribution over current systems.Another object of this invention is not to necessarily neutralize anamine salt functionality but to provide a pH where the monomersdescribed are hydrolytically stable and where the copolymerizationkinetics are most favorable. Other advantages include increased activityand shelf life of the resulting products, increased performance in highpH applications, and production of the material in various formsincluding solutions, solution gels and emulsions.

The invention permits the preparation of novel water treatment polymerscontaining at least a small proportion of cationic functionalityprovided by the comonomer. These new flocculant compositions areobtained by polymerizing ethylenically unsaturated monomers containingquaternary amine functionalities with essentially nonionic monomers toobtain a polymer containing an improved charge distribution in thepresence of acid.

This invention can be applied to polymerizations conducted in aqueoussolutions, solution gels and emulsion products. The polymerization canbe initiated by free radical initiators such as ammonium persulfate,2,2'-azobis(2,4-dimethyl valeronitrile) and by UV light, gamma radiationand other ionizing radiation. One particularly desirable implementationof the subject invention is the production of cationic polymers inemulsion form.

Additional objects and advantages of the invention will become apparentfrom the description and examples provided hereinafter.

BRIEF DESCRIPTION OF THE DRAWING

Illustrated in the figures of Drawing 1 is the effect of the varioustypes and levels of acids on the stability of the charge present on theproduct polymer. The drawing is further discussed in conjunction withExample 9.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The inverse emulsion products of this invention consist of a continuousoil phase composition in which microscopic droplets of a dispersedaqueous phase containing the water soluble polymer are present. Alsopresent in the system are various surfactants which help stabilize theemulsion and aid in the release of the polymer at the point of end use.

Products of this type are commonly manufactured by a process consistingof the steps of raw material preparation, homogenization, reaction andproduct finishing.

Raw material preparation is accomplished by mixing the components of theaqueous and oil phase together in two separate vessels and oftenadjusting the pH of the aqueous phase.

In the case of acrylamide-dimethylaminoethyl methacrylate methylchloride quaternary salt copolymerization, for example, the steps of rawmaterial preparation are as follows:

1. The addition of the required quantities of acrylamide,dimethylaminoethyl methacrylate methylchloride quat, and deionizedwater.

2. The addition to the above mixture of a quantity of acid to adjust thepH to a value between 1.0 and 4.0, preferably between 3.0 and 4.0.

3. The addition of diethylene triamine penta-acetic acid, pentasodiumsalt to chelate the copper present as a polymerization inhibitor in theacrylamide and cationic monomers.

4. The oil phase is prepared by placing the required amount of oil inthe ultimate reaction vessel and mixing in the appropriate water-in-oilemulsifying agents.

Under some conditions, it may be necessary to heat the oil to ensure thegood dissolution of emulsifying agents. This is particularly true in thecase of materials such as sorbitan monostearate and other emulsifyingagents which are solid at ambient temperatures.

Illustrative water-in-oil emulsifying agents that can be used aresorbitan monooleate, sorbitan monostearate, and ethoxylated derivativesof the former.

Oils can be of the general classes of mineral oils, deodorized keroseneor solvents such as xylene. A preferred class of oils are deodorizedkerosenes with an aromatic content below 10%.

5. The aqueous phase is then pumped into the reaction vessel withagitation in the reaction vessel. The addition of aqueous phase to theoil assures proper initial formation of a water-in-oil emulsion.

6. Homogenization of the resulting reaction mass can be accomplished beseveral means. Immersion homogenizers, external recirculation throughcolloid mills or ultrasonic dispersion equipment and pumping thematerial at high pressure through small orifices can all be usedeffectively. The selection of the equipment to be used will, in largepart, be determined by the surface active properties of the water-in-oilemulsion formed in Step 5. The key parameters are the average particlesize and particle size distribution of the resulting emulsion. Normallyit is sufficient that all particles be below 5 microns in diameter andthe average particle size be about 1 micron.

7. The polymerization of the reaction mass must be preceded by an inertgas purge to eliminate dissolved oxygen which suppresses the reaction.Nitrogen is most commonly used for this. Once the dissolved oxygen isremoved, the free radical initiator is added. Various oil soluble azoinitiators are commonly used. Operating temperature and amount ofinitiator should be selected so that the reaction rate is as high aspossible in large scale vessels (250 gallons) within heat transferlimitations to minimize cleaning problems.

8. Once the reaction is completed, a detergent which aids in the releaseof the polymer must be added. This detergent is most typically anethoxylated nonylphenol and it is added at a level of 1.0 to 4.0%relative to the overall reaction mass. This must be added gradually toallow even distribution in the reaction mass. The resulting product isthen filtered to remove any suspended coagulum and packaged.

The effectiveness of the cationic emulsion polymer is evidenced in theexamples presented hereinbelow.

Because of the particularly high molecular weights and activities of thesubject polymers, they are especially effective in applications such asthickening agents, and flocculants as well as in applications such as,centrifuge sludge dewatering where they generally function at lowconcentrations. They show particular advantages, for example, in sewagetreatment to thicken, dewater and remove phosphorus therefrom; inmineral processing to flocculate slimes and slurries and in papermanufacturing to retain pigment, improve strength or alter theconductivity.

The invention also contemplates copolymers and terpolymers obtained bypolymerization of mixtures of these monomers as well as water solublemixtures of such monomers with various other polymerizable monomers inrelative proportions that yield water soluble copolymers. Variouscopolymers may include acrylamide, methacrylamide, acrylonitrile,acrylic acid and salts thereof, dimethylamino ethyl methacrylate andquaternary salts thereof and other ethylenically unsaturated monomers.By selection of monomer combinations, polymers which are cationic,anionic, or amphoteric, can be made as desired.

The following examples are illustrative of the invention. Theenumeration of details in the examples should not be interpreted aslimitations except as may be expressed in the appended claims. Parts areparts by weight unless stated otherwise.

EXAMPLE 1

A cationic copolymer was produced using the following ingredients:

    ______________________________________                                        Material              Quantity                                                ______________________________________                                        Acrylamide (50% aqueous solution) (AM)                                                              110.0 grams                                             Dimethylaminoethylmethacrylate-                                                                     175.0                                                   Methyl Chloride Quat (75% aqueous                                             solution) (QM)                                                                Deionized water       35.0                                                    Paraffinic Solvent    150.0                                                   Ethoxylated Lauryl Alcohol                                                                          8.75                                                    Sorbitan Monooleate   8.75                                                    Ethoxylated Nonylphenol (activator)                                                                 15                                                      Pentasodium salt of diethylenetriamine                                                              0.1                                                     pentaacetic acid                                                              2,2'-azobis (2,4-dimethylvaleronitrile)                                                             0.015                                                   ______________________________________                                    

All components, except surfactants, initiators and oil were combined andmixed while agitated in a vessel until homogeneous to form the aqueousphase. The pH of the aqueous phase was measured and found to be 5.3. Theoil and surfactants were combined in an agitated, temperature controlledreactor.

The aqueous phase was then added to the reactor containing theoil-surfactant blend with mixing. This forms a crude emulsion. Ahomogenizer was then used to decrease the particle size to below 5microns before polymerization.

The emulsion was then purged with nitrogen for about one hour and thenthe reaction mass was heated to 40° C. The initiator was then added andthe reactor was then refluxed for ten hours. Samples were taken duringthe polymerization and analyzed for monomer content by HPLC. When thereaction was substantially complete the activator was added to theemulsion polymer. The results of the monomer analysis are set forthbelow in Table I.

                  TABLE I                                                         ______________________________________                                        Time (hrs)                                                                              AM (%)     QM (%)   d (QM)/d (AM)                                   ______________________________________                                        0.00      11.08      30.70    --                                              2.00      10.19      27.38    3.73                                            4.50      6.93       5.45     6.73                                            5.50      1.92       0.00     1.09                                            6.50      0.40       0.00     0.00                                            7.50      0.22       0.00     0.00                                            ______________________________________                                    

The ratio of disappearance of QM to acrylamide is shown in the fourthcolumn. The ratio should be as constant as possible over the course ofthe reaction to insure good charge distribution.

EXAMPLE 2

The procedure of Example 1 was followed except that hydrochloric acidwas added to adjust the pH of the aqueous phase to pH 3.5. The resultsare summarized in the following Table II.

                  TABLE II                                                        ______________________________________                                        Time (hrs)                                                                              AM (%)     QM (%)   d (QM)/d (AM)                                   ______________________________________                                        0.00      11.64      29.08    --                                              2.00      11.22      24.58    10.84                                           4.50      7.57       10.10    3.96                                            6.00      4.38       0.44     3.03                                            6.50      1.84       0.00     0.17                                            7.00      0.89       0.00     0.00                                            ______________________________________                                    

EXAMPLE 3

The procedure of Example 1 was followed except that succinic acid wasused to bring the pH of the aqueous phase to 4.7. The results aresummarized in the following Table III.

                  TABLE III                                                       ______________________________________                                        Time (hrs)                                                                              AM (%)     QM (%)   d (QM)/d (AM)                                   ______________________________________                                        0.00      12.95      32.66    --                                              2.00      9.89       21.39    3.69                                            4.50      5.34       1.19     4.44                                            6.00      1.41       0.00     0.30                                            7.00      0.52       0.00     0.00                                            ______________________________________                                    

EXAMPLE 4

The procedure of Example 1 was followed except that succinic acid wasused to bring the pH of the aqueous phase 3.5. The results aresummarized in the following Table IV.

                  TABLE IV                                                        ______________________________________                                        Time (hrs)                                                                              AM (%)     QM (%)   d (QM)/d (AM)                                   ______________________________________                                        0.00      11.21      28.16    --                                              2.00      10.47      25.86    3.09                                            4.50      8.00       11.62    5.77                                            6.00      5.09       1.14     3.60                                            7.00      2.19       0.00     0.39                                            7.50      1.12       0.00     0.00                                            ______________________________________                                    

EXAMPLE 5

The procedure of Example 1 was followed except that adipic acid was usedto bring the pH of the aqueous phase 3.5. The results are summarized inthe following Table V.

                  TABLE V                                                         ______________________________________                                        Time (hrs)                                                                              AM (%)     QM (%)   d (QM)/d (AM)                                   ______________________________________                                        0.00      11.14      27.64    --                                              2.00      8.65       16.89    4.30                                            4.50      4.88       1.15     4.18                                            6.00      1.78       0.00     0.37                                            7.00      0.80       0.00     0.00                                            ______________________________________                                    

It is noted that when carboxylic acids are used, the ratios of monomerdisappearance are much more constant indicating that the active cationiccharges are more uniformly distributed.

EXAMPLE 6

A cationic copolymer was produced using the following ingredients usingthe procedure of Example 1:

    ______________________________________                                        Material              Quantity                                                ______________________________________                                        Acrylamide (50% aqueous solution) (AM)                                                              180.16 grams                                            Dimethylaminoethylimethacrylate-                                                                    43.38                                                   Methyl Chloride Quat (75% aqueous                                             solution) (QM)                                                                Deionized water       35.0                                                    Paraffinic Solvent    150.0                                                   Ethoxylated Lauryl Alcohol                                                                          3.85                                                    Sorbitan Monooleate   13.65                                                   Ethoxylated Nonylphenol (activator)                                                                 11.0                                                    Pentasodium salt of diethylenetriamine                                                              0.1                                                     pentaacetic acid                                                              2,2'-azobis (2,4-dimethylvaleronitrile)                                                             0.015                                                   Adipic Acid           1.0                                                     ______________________________________                                    

EXAMPLE 7

The procedure of Example 6 was followed with the exception that 8 gramsof adipic acid were used.

EXAMPLE 8

The procedure of Example 6 was followed with the exception that 12 gramsof adipic acid were used.

EXAMPLE 9

The procedure of Example 6 was followed with the exception that 16 gramsof adipic acid were used.

Samples of the products from Examples 6 through 9 were then stored underambient conditions for a period of four weeks. During the time thesamples were analyzed using a method of charge titration to determinethe cationic content of the polymer (other methods, such as infraredspectroscopy could be suitable). The results are presented below:

                  TABLE VI                                                        ______________________________________                                        Time                                                                          (Weeks)                                                                              Example 6  Example 7 Example 8                                                                              Example 9                                ______________________________________                                        0      12.48      11.98     10.3     12.5                                     1      11.08      12.06     12.5     11.95                                    2      11.67      10.67     8.06     7.84                                     3      13.34      10.74     7.94     6.69                                     4      11.7       10.36     8.87     7.69                                     ______________________________________                                    

As shown from the foregoing data and by reference to the figure of thedrawing, the general conclusion here is that the cationic charge isrelatively stable unitl a high level of dicarboxlic acid is added. Thislevel corresponds roughly to decreasing the pH below 3.

EXAMPLE 10

The results of Examples 1-5 were used to determine the actualdistributions of charge on the polymers by the method described herein.Table VII summarizes the results of this calculation for Examples 1-5.It was found that the polymers produced with no acid or mineral acidshad a weighted standard deviation of the disappearance ratio equal to orgreater than 0.85, while the polymers produced in the presence ofdicarboxylic acids had standard deviations equal to or less than 0.54.This is considered to be about 0.6. Obviously this is a majorimprovement in the charge distribution, and results in a copolymer of AMand QM with a charge distribution uniformity hitherto unattainable.

                                      TABLE VII                                   __________________________________________________________________________    Effect of Acid on Charge Distribution                                         time (hrs)                                                                          AM (%)                                                                             QM (%)                                                                             d (moles AM)                                                                          d (moles QM)                                                                         d (QM)/d (AM)                                                                          d [QM]/d [AM]                                                                         Conversion                    __________________________________________________________________________                                                    (%)                           Example 1 - no acid                                                           0.00  11.08                                                                              30.70                                                              2.00  10.19                                                                              27.38                                                                              0.01    0.02   1.28     1.28    9.39                          4.50  6.93 5.45 0.05    0.11   2.30     2.30    49.87                         5.50  1.92 0.00 0.07    0.03   0.37     0.37    31.85                         6.50  0.40 0.00 0.02    0.00   0.00     0.00    7.04                          7.50  0.22 0.00 0.00    0.00   0.00     0.00    0.83                                                                          98.98                         Standard Deviation = 0.92                                                     Example 2 - HCl                                                                     11.64                                                                              29.08                                                              0.00  11.22                                                                              24.58                                                                              0.01    0.02   3.67     3.67    9.08                          2.00  7.57 10.10                                                                              0.05    0.07   1.36     1.36    39.85                         4.50  4.38 0.44 0.04    0.05   1.04     1.04    30.08                         6.00  1.84 0.00 0.04    0.00   0.06     0.06    12.46                         6.50  0.89 0.00 0.01    0.00   0.00     0.00    4.40                                                                          95.88                         Standard Deviation = 0.84                                                     Example 3 - Succinic Acid pH 4.7                                                    12.95                                                                              32.66                                                              0.00  9.89 21.39                                                                              0.04    0.05   1.26     1.26    28.67                         2.00  5.34 1.19 0.06    0.10   1.52     1.52    47.51                         4.50  1.41 0.00 0.06    0.01   0.10     0.10    17.98                         6.00  0.52 0.00 0.01    0.00   0.00     0.00    3.69                                                                          97.84                         Standard Deviation = 0.32                                                     Example 4 - Succinic Acid pH 3.5                                                    11.21                                                                              28.16                                                              0.00  10.47                                                                              25.86                                                                              0.01    0.01   1.06     1.06    7.33                          2.00  8.00 11.62                                                                              0.03    0.07   1.97     1.97    35.22                         4.50  5.09 1.14 0.04    0.05   1.23     1.23    31.16                         6.00  2.19 0.00 0.04    0.01   0.13     0.13    15.78                         7.00  1.12 0.00 0.02    0.00   0.00     0.00    5.13                                                                          94.63                         Standard Deviation = 0.49                                                     Example 5 - Adipic Acid pH 3.5                                                      11.14                                                                              27.64                                                              0.00  8.65 16.89                                                                              0.04    0.05   1.48     1.48    28.58                         2.00  4.88 1.15 0.05    0.08   1.43     1.43    42.42                         4.50  1.78 0.00 0.04    0.01   0.13     0.13    16.19                         6.00  0.80 0.00 0.01    0.00   0.00     0.00    4.54                                                                          91.72                         Standard Deviation = 0.32                                                     __________________________________________________________________________

EXAMPLE 11

The specific filter resistance test compares the comparative dewateringcapabilities of different polymers on an individual sludge. The methodconsists of adding polymer to the sludge to be dewatered, filtering theflocculated sludge and monitoring the quantity of filtrated drained overtime.

The SFR (specific filter resistance) is calculated by an equationcomparing the filtrated drained over time and a number of parameters:

    t/v=μW°av/2ΔPA.sup.2

Where

t=time

v=volume of filtrate

W°=Weight of solids deposited per unit volume of filtrate

μ=Absolute viscosity of the water

ΔP=Pressure drop across the sludge cake

A=Cross-sectional area of the cake

a=Specific resistance of the sludge cake

Plotting t/v vs v, and all the parameters are known except for a(specific resistance of the sludge cake); a can then be calculated bymeasuring the slope of the t/v vs-Y curve in the initial linear region.

Varying the dosages of the polymer, a series of points with differentSFR's can be found for the polymer of interest on a sludge, showing thedewatering ability of that polymer. By using a different polymer on thesame sludge, a comparison between the two polymers can be observed. Apolymer working at lower SFR's use a lower dose is, according to thiswell accepted test, the more effective product. Further backgroundinformation can be found in Weber, J. Physiochemical Processes for WaterQuality Control, pp. 566-567 Wiley-Interscience Publishers, New York1972.

The products of Examples 1 through 5 were evaluated using the followingtechnique:

Aliquots of 500 milliliters of tap water were placed in 800 milliliterflasks and 2.5 grams each of the products of Examples 1 through 5 wereadded to each of the flaks under the conditions of vigorous mixing. Themixing was continued for one-half hour after the addition of thepolymer.

Quantities of the resulting solution were added to 100 milliliteraliquots of anaerobic digested sludge obtained from the SyracuseMetropolitan Waste Water Treatment Plant. Doses used were in the rangeof 20 to 140 parts per million of polymer.

The resulting polymer-sludge mix was agitated by pouring the mixtureback and forth from one mixing cup to the next twelve times. Theresulting flocculated sludge was then filtered in a 55 milliliterBuchner funnel with a disk of filter cloth serving to retain the sludgesolids. Filtration rates were then measured and the specific filterresistances calculated according to the previous discussion. Results areset forth in Table VIII below.

                  TABLE VII                                                       ______________________________________                                        Dose (ppm)    SFR (gm.sup.2 /sec)                                             ______________________________________                                        Example 1                                                                     1.04E + 02    1.00E + 06                                                      1.20E + 02    5.10E + 05                                                      1.36E + 02    2.35E + 05                                                      1.51E + 02    1.94E + 05                                                      1.67E + 02    5.38E + 05                                                      Example 2                                                                     8.70E + 01    6.50E + 06                                                      1.04E + 02    1.60E + 06                                                      1.20E + 02    4.90E + 05                                                      1.36E + 02    2.60E + 05                                                      1.52E + 02    1.19E + 05                                                      1.67E + 02    6.80E + 04                                                      Example 3                                                                     1.04E + 02    7.00E + 05                                                      1.20E + 02    2.60E + 05                                                      1.36E + 02    7.08E + 04                                                      1.44E + 02    6.10E + 04                                                      1.51E + 02    1.67E + 06                                                      Example 4                                                                     1.04E + 02    9.00E + 05                                                      1.20E + 02    5.90E + 05                                                      1.36E + 02    2.56E + 05                                                      1.44E + 02    1.00E + 05                                                      1.52E +  02   2.28E + 05                                                      Example 5                                                                     1.04E + 02    7.30E + 05                                                      1.21E + 02    2.00E + 05                                                      1.36E + 02    2.70E + 05                                                      1.53E + 02    1.30E + 04                                                      1.29E + 02    8.20E + 04                                                      ______________________________________                                    

It is noted that, in general, the performance of the samples containingcarboxylic acids was superior to those containing mineral acids and thatthe samples with the most favorable reaction rate ratios outperformedthose with the less favorable reaction rate ratios.

It will be understood that various modifications may be effected withoutdeparting from the scope of the invention and the several detailsdisclosed herein as illustrative are not to be construed as placinglimitations on the invention except as may be required by the recitationin the appended claims.

What is claimed is:
 1. A water soluble cationic acrylamide polymerhaving relatively uniform cationic quaternary amine functional unitdistribution comprising a polymer of a monomer of the formula

    CH.sub.2 =RC--CONH.sub.2                                   (a)

wherein R is H or CH₃ and a monomer having quaternary amine units andhaving the formula

    CH.sub.2 ═CHR.sub.1 COO(CH.sub.2).sub.n N(CH.sub.3).sup.+ R.sub.2.sup.-(b)

where R₁ is H or CH₃, n is 2 or 3 and R₂ is Cl⁻ or CH₃ OSO₃ ⁻, whereinsaid polymer is formed by acidifying said monomer (a) with an acidcontaining carboxylate groups having a pKa greater than 1 to provide apH in the range of between about 2.0 and 4.5, and polymerizing withmonomer (b), wherein the weighted standard deviation of the chargedistribution as calculated from measurements of the disappearance ratesof the monomers is less than about 0.6.
 2. The polymer of claim 1wherein the polymer is derived from a monomer mixture which containsalso a different ethylenically unsaturated monomer.
 3. The polymer ofclaim 1 wherein n is
 3. 4. The polymer of claim 1 wherein n is
 2. 5. Thepolymer of claim 1 wherein R is H.
 6. The polymer of claim 1 wherein Ris CH₃.
 7. The polymer of claim 1 wherein the (a) monomer is acrylamideand the (b) monomer is 3-methyacrylamidopropyltrimethyl ammoniumchloride.
 8. The polymer of claim 1 wherein the (a) monomer isacrylamide and the (b) monomer is1-trimethylammonium-2-hydroxylpropylmethacrylate methosulfate.
 9. Thepolymer of claim 1 wherein the (a) monomer is acrylamide and the (b)monomer is dimethylaminoethylmethacrylate methylchloride quaternarysalt.
 10. The polymer of claim 1 wherein said weighted standarddeviation is less than about 0.5.
 11. The polymer of claim 1 whereinsaid weighted standard deviation is between about 0.3 and about 0.6. 12.The polymer of claim 2 wherein said weighted standard deviation isbetween about 0.3 and about 0.6.
 13. The polymer of claim 3 wherein saidweighted standard deviation is between about 0.3 and about 0.5.
 14. Thepolymer of claim 4 wherein said weighted standard deviation is betweenabout 0.3 and about 0.5.
 15. The polymer of claim 14 wherein R is H. 16.The polymer of claim 1, wherein said acid is a dicarboxylic acid. 17.The polymer of claim 16, wherein said acid is adipic acid.
 18. Thepolymer of claim 16, wherein said acid is succinic acid.